Update header image. (#3907)

README.md

-<img src="docs/images/unity-wide.png" align="middle" width="3000"/>
-
-# Unity ML-Agents Toolkit (Beta)
+# Unity ML-Agents Toolkit
 
 [![docs badge](https://img.shields.io/badge/docs-reference-blue.svg)](https://github.com/Unity-Technologies/ml-agents/tree/release_1_docs/docs/)
 
 ([all releases](https://github.com/Unity-Technologies/ml-agents/releases))
 
 **The Unity Machine Learning Agents Toolkit** (ML-Agents) is an open-source
-Unity plugin that enables games and simulations to serve as environments for
+project that enables games and simulations to serve as environments for
 training intelligent agents. Agents can be trained using reinforcement learning,
 imitation learning, neuroevolution, or other machine learning methods through a
 simple-to-use Python API. We also provide implementations (based on TensorFlow)

docs/Learning-Environment-Examples.md

 # Example Learning Environments
 
+<img src="images/example-envs.png" align="middle" width="3000"/>
+
 The Unity ML-Agents Toolkit includes an expanding set of example environments
 that highlight the various features of the toolkit. These environments can also
 serve as templates for new environments or as ways to test new ML algorithms.